Effects Of Microbial Activity On Decomposition Of Chaetomorpha And Nitrogen And Phosphorus Release From Sediments In Swan Lake

In recent years,water eutrophication is increasing on a world scale,and the control of internal pollution has been paid more attention.Microbial activity is an important factor which can affect algal decomposition and nutrient release from the sediments.Rongcheng Swan Lake,a natural lagoon,is blooming massive Chaetomorpha spp.In this paper,the seasonal differences in physicochemical characters of sediments were investigated in Swan Lake,and the effect of microbial activity on algal decomposition and nitrogen and phosphorus release from algae tissue were studied.In addition,the impacts of algal decomposition and microbial activity on nutrient release from the sediments were discussed.The main results are as follows:(1)Difference in microbial activity and alkaline phosphatase activity in sediments from different lake areasThe microbial activity(FDA)and alkaline phosphatase activity(APA)in sediments of algae outbreak areas were both higher than those of non-outbreak areas.Higher FDA was observed in the sediments from the center and the western lake throughout the whole year,while lower FDA was observed at the southern lake.For most lake areas,FDA was low in spring and high in autumn.However,APA in sediment was higher in spring and summer,an lower in winter.In the central lake,the kinds of organic phosphorus bacteria was more than that of inorganic phosphorus bacteria,and the phosphate-solubilizing capacity of the former was also relatively high.(2)Effect of microbial activity in sediment on algal decomposition and nitrogen and phosphorus release from algae tissueMicrobial activity had certain promotion effect on algal decomposition and nitrogen and phosphorus release from Chaetomorpha spp.The algal decomposition rate decreased with time,which was much higher at the early period than that at late period.The decomposition rates in different sediment treatments ranged at 9.49%/d~83.84%/d under non-sterilized conditions,which ranged at 4.93%/d~97.78%/d at the sterilized conditions.During the decomposition period,nitrogen and phosphorus in algae could be released into water rapidly.The release rate of nitrogen and phosphorus at the treatments with sediment was higher that at the treatments without sediments,the former decreased with time.Chaetomorpha spp decomposed quickly at the treatment with sediment in center lake,where microbial activity was high.(3)Effects of microbial activity and algal decomposition on nitrogen and phosphorus release from sedimentsUnder the condition without algae,the concentrations of total nitrogen(TN)and total phosphorus(TP)in water at different treatments changed at the range of 0.42~11.71 mg/L and 0.02~0.32 mg/L,which fluctuated over time during the experiment.While under the condition with algae,TN and TP concentrations were much higher than those without algae,which ranged at 5.43~34.76 mg/L and 0.28~1.80 mg/L,respectively.The concentrations of TN and TP were high in the early stage,which decreased with time.At the end of experiment,microbial activities in sediments were relatively high under the condition with algae.Under the condition with algal decomposition,microbial activity had a obvious effect on nitrogen and phosphorus releases from the sediments in Swan Lake.The release amount of nitrogen and phosphorus from the sediments was high when microbial activity was stronger.(4)Effect of microbial activity on nitrogen and phosphorus release from sediments in different areasMicrobial activity and algal decomposition both promoted ion the release of nitrogen and phosphorus from the sediments.Under the condition with algal decomposition,water TN and TP concentrations at different treatments followed the order of the west-northern lake>the central lake>the southern lake,and great difference among different treatments was observed at the early experiment.Under the same microbial conditions,TN and TP concentrations at the treatments with algae was much higher that those without algae,and TP concentrations ranged at 0.58~1.36 mg/L and 0.06~0.47 mg/L,respectively.The results showed that microbial activity could promote the release of nitrogen and phosphorus from algae tissue and the sediments.In Swan Lake,FDA was high in the sediments at the central and west-southern lake,where Chaetomorpha spp.outbreak frequently.Therefore,the accumulation of a large amount of decomposing algae could lead to a rapid increase in water nutrient level,which must be paid attention during the control of internal pollution.